1. Field of the Invention
The present invention relates to oil and gas well drilling and more particularly to the handling of cuttings that are generated during oil and gas well drilling activity. Even more particularly, the present invention relates to an improved method and apparatus for handling cuttings that are generated during oil and gas well drilling and in oil and gas exploration. Tanks are provided on an oil and gas well drilling platform and on a work boat positioned next to the platform. Both the platform and work boat have vacuum units that help transfer cuttings from the platform to the work boat. Processing units can be used to slurrify or liquify the cuttings, either on the platform or on the boat. The liquified or slurrified cuttings can be treated to obtain a desired particle size and/or viscosity.
2. General Background of the Invention
In the drilling of oil and gas wells, a drill bit is used to dig many thousands of feet into the earth""s crust. Oil rigs typically employ a derrick that extends above the well drilling platform and which can support joint after joint of drill pipe connected end to end during the drilling operation. As the drill bit is pushed farther and farther into the earth, additional pipe joints are added to the ever lengthening xe2x80x9cstringxe2x80x9d or xe2x80x9cdrill stringxe2x80x9d. The drill pipe or drill string thus comprises a plurality of joints of pipe, each of which has an internal, longitudinally extending bore for carrying fluid drilling mud from the well drilling platform through the drill string and to a drill bit supported at the lower or distal end of the drill string.
Drilling mud lubricates the drill bit and carries away well cuttings generated by the drill bit as it digs deeper. The cuttings are carried in a return flow stream of drilling mud through the well annulus and back to the well drilling platform at the earth""s surface. When the drilling mud reaches the surface, it is contaminated with small pieces of shale and rock which are known in the industry as well cuttings or drill cuttings.
Well cuttings have in-the past been separated from the reusable drilling mud with commercially available separators that are known as xe2x80x9cshale shakersxe2x80x9d. Other solids separators include mud cleaners and centrifuge. Some shale shakers are designed to filter coarse material from the drilling mud while other shale shakers are designed to remove finer particles from the well drilling mud. After separating well cuttings therefrom, the drilling mud is returned to a mud pit where it can be supplemented and/or treated prior to transmission back into the well bore via the drill string and to the drill bit to repeat the process.
The disposal of the separated shale and cuttings is a complex environmental problem. Drill cuttings contain not only the mud product which would contaminate the surrounding environment, but also can contain oil that is particularly hazardous to the environment, especially when drilling in a marine environment.
In the Gulf of Mexico for example, there are hundreds of drilling platforms that drill for oil and gas by drilling into the subsea floor. These drilling platforms can be in many hundreds of feet of water. In such a marine environment, the water is typically crystal clear and filled with marine life that cannot tolerate the disposal of drill cuttings waste such as that containing a combination of shale, drilling mud, oil, and the like. Therefore, there is a need for a simple, yet workable solution to the problem of disposing of oil and gas well cuttings in an offshore marine environment and in other fragile environments where oil and gas well drilling occurs.
Traditional methods of cuttings disposal have been dumping, bucket transport, cumbersome conveyor belts, screw conveyors, and washing techniques that require large amounts of water. Adding water creates additional problems of added volume and bulk, messiness, and transport problems. Installing conveyors requires major modification to the rig area and involves many installation hours and very high cost.
Patents that relate generally to well cuttings and/or disposal of well cuttings include U.S. Pat. No. 4,255,269 issued to Timmer and entitled xe2x80x9cMethod and Apparatus for Adapting the Composition of a Drilling Fluid for Use in Making a Hole in the Earth by Rotary Drillingxe2x80x9d. Another patent that relates to drilling and specifically the disposal of drill cuttings is the Dietzen U.S. Pat. No. 4,878,576 entitled xe2x80x9cMethod for Accumulating and Containing Borehole Solids and Recovering Drilling Fluids and Water on Drilling Rigsxe2x80x9d.
The Hansen U.S. Pat. No. 4,867,877 discloses a waste removal and/or separation system for removing liquid and solid wastes simultaneous from waste holding tanks or vessels.
A drill cuttings disposal method and system is disclosed in the Jackson U.S. Pat. No. 5,129,469. In the Jackson ""469 patent, drill cuttings are disposed of by injecting into a subsurface formation by way of an annular space formed in a wellbore. The cuttings are removed from the drilling fluid, conveyed to a shearing and grinding system that converts the cuttings into a viscous slurry with the addition of water. The system comprises a receiving tank and a centrifugal pump for recirculating the mixture of cuttings and water (sea water) between the pump and the receiving tank. A discharge conduit is connected to the pump for moving the viscous slurry to an injection pump for high pressure injection into the formation. In the Prestridge et al. U.S. Pat. No. 5,303,786, drill cuttings a similar earth materials are reduced in particle size, slurried and disposed of from a system which includes a ball mill, a reduced particle receiving tank, a grinder pump and communication with the receiving tank and separator screens for receiving a slurry of particles which have been reduced in size through the ball mill and the grinder pump. The underflow of the separator is suitable for discharge for final disposal, oversized particles are returned to the ball mill and the underflow discharged from the separator is controlled to maintain a certain level in the primary receiving tank. A secondary tank may receive a portion of the underflow to be mixed with viscosifiers and dispersants to maintain a suitable slurry composition for discharge. The system may be mounted on a semi trailer and in weatherproof enclosures with the ball mill, receiving tanks and grinder pump on a first level and the separators on the second level. Receiving hoppers for wet drill cuttings as well as frozen or dried cuttings are provided and water or steam may be mixed with the cuttings and conveyed by a bucket elevator from a first level to a second level of the enclosures.
The Angelle U.S. Pat. Nos. 5,662,807 and 5,846,440 disclose an apparatus and method for handling waste. The apparatus includes a container having disposed thereon a rail member. The apparatus also contains a trolley mounted on the rail. The trolley has operatively associated therewith a handling system that has a wiper that extends into the container. The apparatus may also contain an auger, operatively mounted on the container, adapted for removing the waste from the container. A process for handling a discharged waste slurry is also disclosed. The Angelle patents discuss application to oil and gas well drilling and the fact that drilling fluid is an essential component of the drilling process and that the drilling fluid will contain solids which comprise rock and shale cuttings.
The present invention provides a method for disposal of drill cuttings from an oil and gas well drilling platform. The method includes the steps of separating the drill cuttings from substantially all of the well drilling fluid in which the drill cuttings have been conveyed from an area being drilled.
The cuttings are then transferred to a materials collection area on a drilling platform or tower such as a materials collection trough. The drill cuttings are then transported to a holding tank using a vacuum and a first suction line.
A vacuum is generated within the holding tank using a blower so that drill cuttings are transported from the trough or collections area to the tank via a suction line.
Cuttings are then transferred from the holding tank to a work boat via a flow line. Further treatment such as recycling of drilling mud can be performed on the boat.
The drill cuttings are typically transported directly to a holding tank via a first suction line.
The vacuum is generated by a vacuum generating means or blower that is in fluid communication with the holding tank via a second suction line.
The work boat preferably provides its own holding tank of very large volume such as 100-1000 barrels. The holding tank on the work boat is likewise provided with a blower that pulls a vacuum on the tank to aid in transfer of cuttings from the holding tanks on the platform to the holding tank on the work boat.
In one embodiment, the boat is equipped with treatment units that process the cuttings. The cuttings can be slurried on one deck of the boat and then pumped for storage to another deck area on the boat. In yet another embodiment, the boat is equipped with treatment apparatus that separates and recycles drilling fluids such as more expensive synthetics. In a second embodiment, the work boat collects cuttings transferred to it from the drilling platform. The platform or tower has processing equipment that can slurrify or liquify cuttings to produce a desired particle size or viscosity.